In his most expansive remarks so far about the downing of Malaysia Airlines Flight 17 on Thursday, U.S. President Barack Obama laid out compelling evidence that pro-Russian separatists probably fired the missile that destroyed the airliner and killed all 298 people aboard. But he stopped short of definitively laying the blame on Moscow-backed rebels, a decision that may leave the White House open to criticism that it isn’t responding forcefully enough to an attack that the president himself called an "outrage of unspeakable proportions."

The president’s remarks were more measured and cautious than the word coming from inside the U.S. intelligence community, where there is little doubt that the airliner was brought down by separatists firing a Russian-made, and Russian-provided, SA-11 missile launcher, more commonly known as a Buk. Two U.S. officials, who asked to remain anonymous, said that military intelligence had pinned the attack on the separatists, but that the Pentagon may have conveyed that assessment to reporters before the White House was ready to give a definitive public conclusion.

Military officials have been warning since before the downing of the Malaysia Airlines flight that Moscow-backed separatists in Ukraine have been building up an arsenal of the very kinds of weapons used to shoot down the plane. "What we see in training on the east side of the border [of Ukraine and Russia] is big equipment, tanks, [armored personnel carriers], anti-aircraft capability, and now we see those capabilities being used on the west side of the border," Gen. Philip Breedlove, the supreme commander of NATO in Europe, said at a Pentagon news conference on June 30, more than two weeks before the Malaysia Airlines shoot-down. Breedlove said that the U.S. military had seen Russians training the separatists to use "vehicle-borne" missile systems like the Buk missile, which is mounted on a truck along with a small radar system for tracking airborne targets.

But the Obama administration has been burned before by preliminary intelligence that turned out to be flawed — most famously in the flubbed public explanation for the 2012 attack on the U.S. diplomatic compound in Benghazi, Libya. "I think it’s very important for folks to sift through what is factually based and what is simply speculation," Obama said. He also refused to be dragged into a discussion about further punitive actions against Russia, and he didn’t commit to a new round of sanctions when pressed on the question by reporters. As far as the White House is concerned, the onus is now on the Kremlin to "de-escalate the situation," as Obama put it. But avoiding a forceful response will be much harder if conclusive proof emerges that separatists using weapons given to them by Russia brought down the airliner.

The president came as close as he could to directly blaming Russia for the shoot-down, but stopped just short. "We know that [the separatists] are heavily armed and that they are trained. And we know that that’s not an accident. That is happening because of Russian support," Obama said.

Still, with evidence mounting that the plane was brought down with a Russian weapon that Moscow knowingly provided to the separatists, Obama will soon have to decide how much longer to wait before pinning direct responsibility for the attack on Russian President Vladimir Putin. That could be a turning point in the long shadow war in eastern Ukraine because Obama would come under tremendous pressure to hit Putin hard enough that the Russian strongman brings his meddling in Ukraine to a stop.

Obama made clear that day might still be a ways off when he said that an investigation into the crash, which could prove definitively who shot down the plane, wouldn’t be finished quickly. "The investigation is going to be ongoing, and I think what we’ll see is additional information surfacing over the next 24 hours, 72 hours, the next week, the next month," Obama said. It wasn’t a rallying cry, but it gave the president breathing room to consider a range of responses, which could include new economic sanctions or even military aid to Ukraine.

But in Obama’s hesitation, some saw an opportunity to form a better strategy for countering Putin than anything the administration has devised to date.

Adrian Karatnycky, a senior fellow with the Transatlantic Relations Program at the Atlantic Council, said it "enhances the credibility of the United States" to say that the preliminary evidence points strongly to Russian involvement but then call for an international investigation to ascertain all the facts. (Obama said that he’d dispatched aviation crash scene experts from the FBI and the National Transportation Safety Board to Ukraine and that they were standing by to lend assistance at the Ukrainian government’s request.)

"I don’t think this is a concession or a walking back or a sign of weakness," Karatnycky said in a conference call Friday afternoon, July 18, shortly after Obama’s speech.

John Herbst, who served as the U.S. ambassador to Ukraine during George W. Bush’s administration, agreed that Obama shouldn’t be held to a timetable or rush to make an accusation that he might have to amend later. He noted that Bush officials waited for days after the 9/11 attacks to conclusively identify al Qaeda as the culprit.

Obama may have also bought Putin some time to change course in eastern Ukraine. Obama made clear that he expects Putin to decide the fate of the conflict, but he posed no ultimatums or set any "red lines," as he did last year in Syria with arguably disastrous political consequences.

"If Mr. Putin makes a decision that we are not going to allow heavy armaments and the flow of fighters into Ukraine across the Ukrainian-Russian border, then it [the fighting] will stop," Obama said. "And if it stops, then the separatists will still have the capacity to enter into negotiations and try to arrive at the sort of political accommodations that Mr. Putin himself says he wants to see. He has the most control over that situation, and so far, at least, he has not exercised it."

Karatnycky said Putin has to make "a fateful choice" between continuing to supply the rebels with weapons and training and telling them to stand down while reducing his aid to the fighters. In recent weeks, new weapons have been spotted flowing into eastern Ukraine from Russia. But at the same time, Putin has been "preparing his people for a possible retreat," said Herbst, the former U.S. ambassador to Ukraine, who noted that leading public figures in Moscow are now calling on Russia to stop supporting the rebel forces, criticism that Putin hasn’t tried to refute or silence.

Still, the analysts said that it would be dangerous for Europe and the United States to hold off on hammering Putin for what appears to be his clear responsibility, even if indirect, for the shoot-down. "A clear line needs to be drawn now so Putin realizes what he’s doing in Ukraine is not acceptable. And if the Europeans won’t do it, the United States can," said Herbst. "We don’t want revisionist powers to think that they can take territories … without punishment."